PROJECT SUMMARY Stereotype threat occurs when people fear being judged through the lens of a negative, self-relevant stereotype. Problematically, in response to this, people often underperform compared to their potential. Although stereotype threat is a well-documented phenomenon, previous studies examining it in older adults have almost exclusively examined cognitive performance. This is surprising because there are also many negative stereotypes about older adults' physical abilities; older adults are often stereotyped as being slow, weak, feeble, and frail. Despite the fact that older adults are actually more worried about age-related physical declines than they are about cognitive declines, it is currently unclear how these stereotypes affect older adults' physical performance. To date, only two studies have examined this question and their results are contradictory. In addressing the understudied question of how ageist stereotypes about frailty affect older adults' physical performance, the current study focuses on walking performance. Walking may seem like a simple activity, but it is actually a biologically complex task that involves the interplay of multiple motor and cognitive systems. When any one of these systems is not working properly, markers of walking ability, such as gait speed, decline. Because of this, gait speed is a powerful predictor of morbidity and mortality in older adults. In fact, its predictive value is so strong, that many have called for gait speed to be considered an additional vital sign that is routinely assessed for older adults. Although self-selected walking speed has potential clinical utility, an important, but unanswered question is how patients' expectations and concerns affect their performance. In examining this, we draw upon the biopsychosocial model of challenge and threat. According to this model, in motivated performance situations people appraise the demands of the task (e.g., `how difficult is the task?') as well as their personal resources (e.g., `do I have the skills to perform well?'). When people perceive the demands as greater than their resources, they experience threat. When people perceive their resources as greater than the demands, they experience challenge. This in turn affects performance; threat appraisals impair performance whereas challenge appraisals improve performance. However, no previous study has tested this model in older adults. To address this, in the current study, older adult participants will be asked to complete ?difficult? and ?easy? walking tasks. During difficult tasks, we predict that age-based evaluations will be perceived as ?threats? and lead to slower gait speed. In contrast, during easy tasks, we predict that age-based evaluations will be perceived as ?challenges? and lead to faster gait speed (in contrast to the stereotype). We will also examine whether effects depend upon the method of instantiating the age-based evaluation, and whether age-based evaluations also affect other gait biomechanical measures associated with fall risks. Results will add to our knowledge about how ageism affects older adults' health and fall risks and will improve best practices for administering walking assessments.